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Limestone stalactites and stalagmites are formed in caves by the following reaction:

Ca2 + (aq) + 2 HCO3–(aq) CaCO3(s) + CO2(g) + H2O(l)

If 1 mol of CaCO3 forms at 298 K under 1 atm pressure, the reaction performs 2.47 kJ of P–V work, pushing back the atmosphere as the gaseous CO2 forms. At the same time, 38.95 kJ of heat is absorbed from the environment. What are the values of ∆H and of ∆E for this reaction?

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Jarrod Robel
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Related questions

Limestone stalactites and stalagmites are formed in caves by the following reaction: Ca2+(aq)+2HCO−3(aq)→CaCO3(s)+CO2(g)+H2O(l) If 1 mol of CaCO3 forms at 298 K under 1 atm pressure, the reaction performs 2.49 kJ of P−V work, pushing back the atmosphere as the gaseous CO2 forms. At the same time, 38.95 kJ of heat is absorbed from the environment.

1. What is the value of ΔH for this reaction? Express your answer using four significant figures.

2. What is the value of ΔE for this reaction? Express your answer using four significant figures.

Practice problems for exam 2 ______________

Useful Information:

h=6.626×10-34J·s.; c=3.0×108 m/sec; E=h ; E= hc ,  = h/mv; 1J = 1 kg-m2/s2 

mass of electron = 9.11 × 10-28 g, E= q + w ; 1 cal = 4.184 Joules Please Show all Work

1. Which of the following substances have standard heats of formation that are equal to zero by definition (circle your answers): H2(g), H(g), O3(g), H2O(s), H2O(l), Hg(l), Hg(s), Hg(g).

2. Limestone stalactites are formed in the reaction: Ca2+(aq) + HCO3-(aq) ïƒ CaCO3(s) + CO2(g) +

H2O(l)
If one mole of CaCO3 is produced at 298 K under one atmosphere of pressure, the reaction performs 590 calories of expansion work, pushing back the atmosphere as CO2 is formed. At the same time, 9310 calories of heat are absorbed from the environment. What is E in Kcal/mole for CaCO3.

3. What is the minimum wavelength of light in Å (1 Å = 10-8 cm) needed to provide enough energy per quantum to rupture the chemical bond in hydrogen iodide (HI). The bond dissociation energy of HI is 71.4 Kcal/mole.

1

4. Sketch the shape and orientation of the following types of orbitals: s, px, dxy, dz2, dx2-y2

5. Give the values of (n) , (l) and (ml) for each orbital in the 4p subshell.

6. Write the complete electron configuration for the following: Ti 2+_____________________________________ Cr_______________________________________

N______________________________________

7. Calculate the standard enthalpy of formation (  Ho) for diamond from graphite [i.e. C (graphite) ïƒ C (diamond)] given that:

C (graphite) + O2 ïƒ CO2 (g) (  Ho = -393.5 KJ/mole) C (diamond)] + O2 ïƒ CO2 (g) (  Ho = -395.4 KJ/mole)

If 1.0g of graphite is converted to diamond, what is the energy change? Is this an endothermic or exothermic reaction?

2

8. An 160 pound astronaut on his way to Mars is buzzing along at 10,000 miles per hour. (a) Express his weight in grams (one pound = 454 grams) so that you can calculate the astronaut’s wavelength (1mile/hour = 44.7 cm/sec)

(b) Suppose the astronaut detects outside his spacecraft a proton (m=1.7 x 10-24 g) from a “solar wind” moving at exactly the spacecraft velocity. What is the proton wavelength is in Å (1 Å = 10-8 cm.

9. What is the maximum number of electrons that can occupy each of the following subshells? a) 3d_________________ b) 1s____________________ c) 2p ____________________

10. Identify the element represented by the following electronic configuration.

a) [Ne] 3s2____________________

b) What is the electron configuration for the first excited state of this atom.______________

11. Determine the number of valence electrons for each element.
(a) Br___________ (b) Na _________ (c) Sn __________

3

12. 175 g of Fe at 15.0oC is mixed with 225 g of H2O at 95.0oC. What is the final temperature of the mixture? The specific heats of iron= 0.448 J/g oC and water = 4.184 J/g oC). (keep in mind the following: heat gained + heat lost = 0 and q=mass x heat capacity x T)

13. (5 pts) Calculate values of ΔHrxn for the following reactions: CS2(g) + 3O2(g)  CO2(g) + 2SO2(g)

The heat of formation for the following substances is given in kJ/mol:

CS2 CO2 SO2 117.4 -393.51 -296.83

14. (6 pts) Use the electron configuration of Li and Be and determine which element has the greatest second ionization energy. Defend your answer.

4

15. Mark beside each of the following processes either “exo” or “endo” according to whether you think the process will release heat or absorb heat.

a. Ca(g) ïƒ Ca(g)+2 + 2e-
b. I(g)+1e-ïƒ I(g)-1
c. Ca(g)+2 + S(g)-2 ïƒ CaS(s) d. I2(g)ïƒ 2I(g)

( ) ( ) ( ) ( )

16. (6 pts) In each of the following pairs, which of the two species is larger?
a) O-2 or Na+ b) Ti+4 or Ti+2 c) B or C d) N or N-3

17. Write down the Lewis dot structure for the following (a) N_______________ (b) Ne________________

18. THE BORN HABER CYCLE: I may have a problem on the Born Haber cycle. Please check my lecture notes to see how to set up the process and then calculate the lattice energy from the various thermodynamic quantities such as in the NaCl example below;

 H  f NaCl = -411KJ

Na(s)  Na(g)  H =108KJ
1⁄2 Cl2  Cl(g)  H = 122KJ Ionization Energy of Na  H = 496 KJ Electron affinity of Cl  H = -349KJ

What is the balanced chemical equation for the reaction used to calculate ΔH∘f of CaCO3(s)? If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively without indicating allotropes. Use (aq) for aqueous solution. Express your answer as a chemical equation. The standard enthalpy of formation (ΔH∘f) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. The standard conditions are 1 atm pressure, a temperature of 25 ∘C , and all the species present at a concentration of 1 M . A "standard enthalpies of formation table" containing ΔH∘f values might look something like this: Substance ΔH∘f H(g) 218 kJ/mol H2(g) 0 kJ/mol Ca(s) 0 kJ/mol Ca2+(aq) −543 kJ/mol C(g) 71 kJ/mol C(s) 0 kJ/mol N(g) 473 kJ/mol O2(g) 0 kJ/mol O(g) 249 kJ/mol S2(g) 129 kJ/mol

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